Polishing pad and methods of improving pad removal rates and planarization

ABSTRACT

A method of improving a removal rate of a pad includes producing a body of a pad of polyurethane from a mix; and introducing into the mix an additive which decreases an elastic rebound of the pad so as to increase a chemical-mechanical planarization removal rate; and using as the additive a substance which at least contains starch. In another embodiment, in a CMP process that includes removing a barrier and buffing a polyurethane after a bulk copper removal process, a polishing pad is used having a shore D hardness less than 35% and having at least one layer made from a mix composed of at least one of a prepolymer with an isocyanate concentration of between 6.5% and 11.0% to achieve a molal concentration, and a monomer in combination with an addition of isocyanate to achieve the substantially same molal concentration.

BACKGROUND OF THE INVENTION

The present invention generally relates to polishing pads, and, inparticular to chemical-mechanical polishing (CMP) with a slurry.Moreover, the present invention relates to methods for increasing theCMP removal rate of polishing pads, improving the planarization of workpieces by polishing pads, and improving the General PlanarizationEfficiency of polishing pads.

CMP is a process step in the semiconductor fabrication sequence that hasgenerally become an integral part of the manufacture of semiconductorwafers. CMP is used in a variety of applications in the semiconductorfabrication sequence. For example, CMP is used in applications referredto as “oxide” or “ILD/PMD”, “STI”, “copper”, “barrier”, “poly” and“tungsten”. These terms generally indicate the type of material that isbeing removed. The CMP process preferably is configured to expedientlyremove material and planarize the surface, while leaving it defect freeand contamination free. Each of these applications may use a differentslurry, and therefore the removal mechanism is generally different foreach application. For that reason, the optimal condition of each of theapplications tends to be different as well.

In each of these CMP processes, a silicon substrate is placed in directcontact with a moving polishing pad. A wafer carrier applies pressureagainst the backside of the substrate, usually while simultaneouslyrotating the pad. During this process a slurry is made available, and isgenerally carried between the wafer and the pad by the motion of thepad. The composition of the slurry may vary from one CMP application toanother. In general, slurries that are designed to remove insulatingmaterials consist of water, an abrasive and an alkali formulationdesigned to “hydrolyze” the insulating material. Copper slurries on theother hand, generally comprise a combination of: water, an abrasive, anoxidizing agent, a complexing agent, and a chemical to passivize thesurface. A typical slurry often has very low removal rate on a materialit was not designed to remove.

The CMP polishing pad preferably performs a plurality of engineeringfunctions. The pad may desirably be configured to polish at a highremoval rate, planarize short (<100 micrometer) distances, planarizelong (>100 micrometer) distances up to a certain Planarization Length(see below) determined by the quality of the silicon substrate, notplanarize beyond that length, transport slurry, maintain the samefriction with the wafer for wafers polished sequentially and withoutinterruptions for hundreds of wafers, clean the wafer surface, notscratch the wafer surface, be replaceable in minimal time, and/or otherfunctions.

Thus, it is desirable to develop methods of making a pad that canimprove one or more of these functions of polishing pads. In particular,it is desirable to improve the removal rate of the polishing pad, toimprove the planarization of work pieces, and to improve the GeneralPlanarization Efficiency of polishing pads.

In this regard, various aspects of the present invention contemplateboth short and long range planarization. Generally, long rangeplanarization is controlled by the bulk properties of the pad and shortrange planarization is controlled by the surface properties of the pad.A concept useful in describing long range planarization is thePlanarization Length (L), defined as a lateral dimension characteristicof the pad's ability to planarize. Intrinsic to this concept isPreston's equation, which maintains that when polishing, the removalrate is proportional to force. There are significant deviations to thisrelationship, but it holds generally. A feature that is to be planarizedmay be modeled as an upraised element. A polishing pad will try toplanarize this feature, and will succeed in doing so when the pressureexerted by the pad at the top of the feature exceeds the pressureexerted adjacent to the feature. According to the Preston equation, theremoval rate at the top of the feature will exceed the removal rateadjacent to the feature and over time the feature will decrease inheight with polishing. One definition of planarization length is thedistance from the feature that the pressure has increased to 1/e of thepressure infinitely far from the feature (e is ln(10)).

Short range planarization has no analog to L. Since the short rangeplanarization is affected by the surface properties, it can varydramatically using the same polishing pad by varying the amount ofdiamond conditioning received by the pad, an action that affects thepad's surface roughness. However, generally the pad surface isconditioned for the purpose of maintaining the removal rate. Thereforewith regard to short range planarization, the engineering constraintplaced on the pad is rather results-oriented. If written, it would readsomething like, “. . . when consistently using a standard conditioningprocess the pad should exhibit adequate removal rate as well as highshort range planarization . . . ”. Because of this, the short rangeplanarization requirement generally comes from empirical results. Forthe copper application, these results would typically be expressed indishing, which describes the amount of material removed from a narrowcopper line. For oxide applications, the results would typically beexpressed by the planarization performance of a test structure designedto measure short range planarization.

Various U.S. patents contemplate improvements in planarization. See,James, U.S. Pat. Nos. 6,454,634, 6,582,283, 6,736,709 and 6,749,485.While James offers an example of an additive that allegedly achieves adesired high KEL value, the teachings and data support the desiredproperty only for what has been described above as short rangeplanarization, namely planarization which occurs over a distance of lessthan 100 micrometers.

Thus, it is desirable to develop formulations which improve both shortand long range planarization.

A specific application of CMP is known as “copper CMP,” which entailsthe polishing of a copper film deposited on the work surface of asemiconductor wafer. The copper is typically deposited through the useof electro-deposition, and is typically deposited on a surface in whichsubmicron channels in the underlying oxide layer have been created. Thecopper is deposited in the channels as well as on top of the areasbetween channels (the “field”). The copper deposited in the fieldbetween channels is often called the “overburden.” A “barrier layer” isprovided on the oxide surface before depositing the copper since thecopper would otherwise diffuse into the oxide layer and potentiallyreach the sensitive silicon substrate below, destroying the transistors.Accordingly, the barrier clads the copper channels, preventing diffusionof the copper into the oxide. Typical materials for the barrier layerare tantalum (Ta) and tantalum nitride (TaN). During copper CMP, boththe copper overburden and the barrier layer are removed from the fieldby polishing, leaving the copper in the channels to act as conductinginterconnecting lines.

The objective of the CMP process is to remove substantially all of thecopper from the field area and leave the copper in the trenches at thelevel of the oxide. The surface of the copper in the channels ispreferably flat and substantially without oxidation, contamination orcorrosion on its surface. These conditions are also desirable for otherlarger areas of copper known as “bond pads,” which allow probes to makecontact with the conductor, and are typically 100 um by 50-75 μm indimension. The process is usually performed in three steps, involvingthree rotating platens normally found on commercially available CMPtools. The steps include: 1) removal of the bulk copper; 2) removal ofthe barrier layer; and 3) buffing of the final surface to removesubstantially all residue and to passivate the copper surface. Afterthese three steps, the wafer may be cleaned and dried prior to furtherprocessing. Often, the step of removal of the copper is divided into twosteps. In the first step, half or more of the copper film is removedleaving the surface substantially planar. In the second step, theremainder of the copper is removed, leaving only barrier material.

There are, therefore, two primary process sequences used on athree-platen tool during conventional copper CMP. In the first sequence,Sequence #1, Platen 1 removes bulk copper to the barrier material,Platen 2 removes the barrier material and Platen 3 buffs. In the secondsequence, Sequence #2, Platen 1 removes bulk copper, Platen 2 finishescopper removal, and Platen 3 removes barrier material and buffs. Therealso exist small variations to these two sequences that could includevariations in the chemistries and slurries used, the processingconditions and times, and the exact division of all the required steps.The polishing pads and slurries/chemistries used in these three stepsare generally different.

In one example, a typical way to carry out process Sequence #1 could beto use the following: Platen 1) An IC1000 pad (such as supplied by Rohmand Haas) and a copper slurry such as Cabot 5001; Platen 2) An IC1000pad and a barrier slurry such as Hitachi T-605; and Platen 3) A Politexpad (such as supplied by Rohm and Haas) and water or water and apassivize chemical such as BTA. Conversely, a typical way to carry outprocess Sequence #2 could be to use the following: Platen 1) An IC1000pad and a copper slurry such as Cabot 5001; Platen 2) An IC1000 pad anda copper slurry such as Cabot 5001; Platen 3) A Politex pad and abarrier slurry such as Hitachi T-605, followed by a rinse with water orwater and BTA for passivation.

Step 3 in the last case could also be performed with an IC1000 pad, butis much more typically performed with a Politex pad. The disadvantage ofusing the Politex for this purpose is that the pad is basically too softfor the application. A typical Politex pad is composed of severallayers. The bottom layer is a polyurethane impregnated polyester felt.The next layer is a very porous urethane, and the top layer consists ofvertical urethane structures having tapered pores which are wider on thebottom and narrower on top.

Although the softness of the pad is advantageous in delivering a verynice final surface (buff), both clean and scratch-free, the net resultof using this pad for the barrier removal step is that the resultingplanarity of the wafer is poor. As a barrier remover, the pad is exposedinitially to both copper and tantalum simultaneously and later when thebarrier is cleared, to oxide, copper and tantalum simultaneously. A padwith poor planarizing properties will do a poor job of uniformlyremoving these materials. This nonplanarity can result in bridging (aconductive material remaining where it is supposed to be removedresulting in undesired electrical contact), dishing/erosion (materialbeing removed by the process that should remain in place causing anincrease in resistivity if it is copper or shorts if it is oxide), orundesirable surface features that encourage bridging.

Another issue with the use of the Politex pad is the relatively lowlifetime of the pad. In the presence of certain chemicals, the pad willtend to lose integrity, resulting in shortened lifetime. In general, theblown polyurethane material is chemically inert, and is not known todisintegrate in the presence of any of the chemicals it is normallyexposed to during CMP.

The alternative case, using the highly planarizing, highly inert, IC1000on the third platen will result in a very planar surface without theproblems listed above, but with a much higher rate of scratching.Scratching, of course, is unacceptable as it can result in shorts(bridging) and opens (a conductive line interrupted). Thus a need existsfor a pad having various properties in a range between those offered bythe Politex and the IC1000 pads.

In light of these issues Sequence #1 apparently satisfies allrequirements; however, it is very slow. It has a much slower throughput(“tpt”), and thus the polishing equipment is poorly utilized. Just likeany assembly line, the tpt of a tool is a function of its slowest step.Generally, the robots moving the wafers from station to station on suchtools (see, for example, the Mira Mesa, supplied by Applied Materials)are fast. The slowest step is typically the slowest of the platen steps.Since Sequence #1 involves bulk removal of the copper at the firstplaten, that platen is likely the tpt limiter. It is not uncommon forthat first step to take 3 or 4 minutes, resulting in a maximum tpt ofthe tool of 15-20 wafers per hour (“wph”). A higher tpt is generallydesired.

Accordingly, there is a need for an improved CMP pad and an improvedmethod of copper CMP providing increased tpt and improved bulk copperremoval and/or planarization.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide amethod of improving the chemical-mechanical planarization removal rateof polishing pads, to provide an improved method of chemical mechanicalpolishing, and to provide an improved polishing pad.

In accordance with one aspect of an exemplary embodiment of the presentinvention, the method of improving a removal rate of a pad, comprisesthe steps of: producing a body of a pad of which at least the top layeris polyurethane; introducing into the body an additive which decreasesthe ER of the pad so as to increase a chemical-mechanical planarizationremoval rate; and using as the additive a substance which at leastcontains starch. In accordance with still a further feature of thepresent invention, said using step includes introducing substantiallyone pound of starch in a 25 pound mix to reduce the elastic rebound byapproximately eight percentage points.

In accordance with various aspects of the present invention,introduction of at least a substance containing starch into thepolyurethane body of the pad significantly decreases the elastic reboundand as a result the chemical-mechanical planarization removal rate ofthe pad is increased.

In keeping with these objects and with others that will become apparenthereinafter, one feature of the present invention includes a method ofcopper CMP for copper film deposited on a surface of a semiconductorwafer. The method comprises the steps of removing a bulk copper to abarrier; substantially removing the barrier; and subsequently buffing,and wherein said barrier removing and buffing includes using apolyurethane polishing pad having at least one layer fabricated from amix composed of a prepolymer with an isocyanate concentration of betweenabout 6.5% and about 11.0% or from a monomer and an addition ofisocyanate to achieve substantially the same molal concentration, inwhich a shore D hardness of the layer is less than about 35%.

An exemplary embodiment of the present invention includes a polishingpad for removal of a barrier and subsequent buffing in CMP of a copperfilm deposited on a surface of a semiconductor wafer. The polishing padis fabricated from a mix composed of the polymer with an isocyanateconcentration of between about 6.5% and about 11.0% or from a monomerand an addition of isocyanate to achieve substantially the same molalconcentration, and has a shore D hardness less than about 35%.

The novel features which are considered as characteristic of the presentinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present invention may be derived byreferring to the detailed description and claims when considered inconnection with the Figures, wherein

FIG. 1 illustrates a planarization of urethane polishing pads as afunction of NCO concentration produced in accordance with the presentinvention; and

FIG. 2 is a plot illustrating a relationship between a hardness of a padand a number of scratches.

DETAILED DESCRIPTION

The description that follows is not intended to limit the scope,applicability or configuration of the invention in any way; rather, itis intended to provide a convenient illustration for implementingvarious embodiments of the invention. As will become apparent, variouschanges may be made in the function and arrangement of the elementsdescribed in these embodiments without departing from the scope of theinvention. It should be appreciated that the description herein may beadapted to be employed with alternatively configured pads havingdifferent shapes, components, and the like and still fall within thescope of the present invention. Thus, the detailed description herein ispresented for purposes of illustration only and not of limitation.

In accordance with one aspect of an exemplary embodiment of the presentinvention, a method is provided for improving the removal rate of apolishing pad. Although removal rates may be affected by the compositionof the slurry used with the pad, several pad-related factors affectremoval rates as well. For example, grooves can improve removal ratesby, for example, delivering the slurry to the wafer-pad interface.Various patterns, pitches, widths and depths of these grooves may bealso affect removal rates. Removal rates are also related to thefriction which exists between the wafer and the pad in the presence ofthe slurry. This friction differs for different pads and can be affectedby factors such as the size of pores in the pad, the density of the pad,the material composition of the pad, and/or the like.

Generally, the pads used for CMP are anelastic. An anelastic materialexhibits both elastic and inelastic properties. A measure of the amountof inelasticity of a material is the Elastic Rebound, or the ElasticRecovery (ER). When compressed and released, the fractional amount ofrecovery after a set period of time is the ER. The higher the elasticrebound, the more elastic the material, while the lower the elasticrebound the more plastic is the material. In accordance with one aspectof an exemplary embodiment of the present invention, polyurethane padsand oxide wafers exhibit CMP removal rates that have been found to bestrongly negatively correlated with ER.

Thus, in accordance with one aspect of an exemplary embodiment of thepresent invention, a method of improving the removal rate of a polishingpad includes constructing the pad to have a lower ER and thus a higherremoval rate. It has been found that the ER of a pad may be lowered byadding starch to the pad components during the mixing of the padingredients (as described more fully below).

Although the introduction of starch into a urethane mix is known for avariety of purposes, it has not been used to improve removal rates inpolishing pads. Starch is a known urethane additive, for example toincrease biodegradability (e.g. U.S. Pat. No. 6,228,969), improve flameretardance and to enhance foaming, (e.g. U.S. Pat. No. 4,374,208).

In accordance with one aspect of an exemplary embodiment of the presentinvention, a CMP pad may comprise, in addition to other components, astarch. For example, a CMP pad may comprise: 20 lbs ADIPRENE L325 LiquidPolyether Urethane from Crompton Uniroyal, 4.7 lbs MOCA(4,4-methylene-bis-chloroaniline), 0.5 lb L-6100 silicone surfactantfrom GE Silicones, and 1 lb starch.

Furthermore, other quantities of the aforementioned components may beused, and the relative proportions may be varied. Moreover, it will beappreciated that starch may be added to other combinations of componentstypically used to create polyurethane pads. In accordance with oneexemplary embodiment of the present invention, the method comprises thesteps of mixing, for about 5 minutes, the starch (or a starch-containingadditive) together with the L-325 Liquid Polymer Urethane and with theL-6100 silicone surfactant. The method may further comprise the step ofmixing (for about one additional minute) an accelerant, such as MOCA,with the mixed starch/L-325/L-6100. The method may further include thesteps of pouring the mix into a mold, curing it at room temperature for15 minutes, placing it into an oven at a temperature of approximately250° F. for approximately 8 hours, cooling the resultant cake andslicing it with a skiving-type blade. The slices are then fashioned intopolishing pads through additional steps such as grooving, applyingadhesive and/or applying a subpad.

In accordance with one exemplary embodiment of the present invention, ascompared with a pad made of the same components but without starch, whenone pound of starch is introduced into the mix, the Elastic Rebound ofthe pads is reduced by a full eight absolute percentage points, fromabout 94% to about 86%, with an r-square value of approximately 66%. Inanother exemplary embodiment, if the amount of starch added to the mixis only 0.5 pound of starch, as compared with a non-starch pad the ERmay be reduced from approximately 94% to approximately 90%.

Thus, a new method of improving the removal rate has been presented. TheCMP removal rate is increased by reducing the elastic rebound of the padthrough the addition of starch or a starch like substance to the padduring its formation. Furthermore, in accordance with various aspects ofthe present invention, planarization of the work piece may also beimproved.

The measurement of planarization may be made using planarization teststructures, which are topographical structures which contain regularperiodic arrays arranged in regions of different pitch and width. Due topractical limitations related to metrology, the smallest of these toyield an accurate measurement has a 100 micrometer pitch at 50% density(i.e. alternating high and low structures of equal width) and thelargest had a 500 micrometer pitch at 50% density. Planarizationcapability is measured by a repeating sequential polish/measure actionin which the remaining amplitude and the average amount of oxide removedis recorded for each step. The sequence is complete when the structureis planarized below a “noise” level. This sequence yields a curve whichcan be further reduced to single figure of merit of planarization calledthe Planarization Efficiency. In order to capture both short and longrange planarization together, and in accordance with one aspect of anexemplary embodiment of the present invention, a parameter has beendeveloped called the General Planarization Efficiency (GPE) whichconsists of the average of the short and long range efficiencies. TheGPE ranges from 0% to 100%, in which 0% represents no planarization atall (i.e. perfect etching), while 100% represents perfect planarization(material removed only from high areas, none whatsoever from low areas).In an exemplary embodiment of the present invention, the GPE is improvedthrough the methods described herein.

In this regard, and in accordance with yet another aspect of anexemplary embodiment of the present invention, urethane polishing padsare produced by combining a basic polyol resin with an isocyanate(“NCO”). It is to be understood that the whole pad can be produced inthis way or only its working layer, in the event when the pad is amulti-layer pad. In a new and special way, the isocyanate is introducedwith a concentration of between about 6.5% and about 11.0% into thebasic resin.

Tests have been conducted to determine the planarization of the padproduced in accordance with the present invention. Four polishing padshave been tested, in particular a polishing pad L-100 with isocyanateconcentration of 4.0%, a polishing pad L-200 with isocyanateconcentration of 7.5% and L-325 with isocyanate concentration of 9.5%from the Adiprene series, and resin 2505 with isocyanate concentrationof 11.6% from the Royalcast series, all from Crompton Uniroyal Chemical.As shown in FIG. 1, when the urethane polishing pads with isocyanateconcentration between about 6.5% and about 11.0% were tested, theyachieved the planarization within the range of about 72% to about 95%.

A breakdown of the data into groups normally expected to affectplanarization does not alter the result. For example, grooving is knownto generally negatively affect the GPE of the pad by structurallyweakening the surface. However, the aforementioned planarization rangewas found to hold both for pads with and without grooving. It is alsoknown that the use of a soft subpad can negatively affect the GPE (byvirtue of its effect on the long range planarization). Again in thiscase the results were unaffected when considering solo pads and padstacks separately. It is therefore understood that the NCO concentrationcontrols physical properties of the pad which affect both the short andthe long range planarization capability.

In accordance with an advantageous feature of the present invention, theconcentration of the isocyanate can be within a range of about 6.5% toabout 8.5%. In this case the urethane pad or its working layer is softerand suitable for barrier buff. In accordance with another preferablefeature of the present invention, the concentration of the isocyanatecan be within a range of about 8.5% to about 11.0%. In this case theurethane pad or its working layer is harder and is suitable forinterlayer dielectric.

The urethane pad or its layer can be composed of polyester polyurethaneor a polyether polyurethane. Furthermore, the urethane pad or itsworking layer can contain abrasive particles which may comprise one ormore of the following components: silica, alumina, ceria, titania,diamond, and silicon carbide. Alternatively, the urethane pad or itsworking layer can be absent of abrasive particles. In addition, theurethane pad or its working layer in accordance with the presentinvention may also include a filler.

The above presented ranges of planarization are highly efficient for theurethane polishing pads. As can be seen, if this isocyanateconcentration is less than about 6.5% and more than about 11.0%, theplanarization property of the urethane polishing pads worsens.

Furthermore, with respect to CMP of copper, in one exemplary embodimentof the present invention, a method is provided for improving CMP of acopper film deposited on a surface of a semiconductor wafer. The methodmay, for example, comprise the steps of removing the bulk copper to abarrier; removing the barrier; and subsequently buffing, wherein saidbarrier removal and buffing include using a polyurethane polishing padfabricated from a mix composed of a prepolymer or a monomer and anaddition isocyanate to achieve substantially the same molalconcentration, in which a shore D hardness is less than about 35%. In apreferred embodiment, the isocyanate concentration is between about 6.5%and about 8.5%, the smaller value generally leading to a softerpolishing pad.

The present invention also relates to a polyurethane polishing pad forremoval of a barrier and subsequent buffing in a chemical mechanicalpolishing process of a copper film deposited on a surface of asemiconductor wafer, the polishing pad fabricated from a mix composed ofprepolymer with an isocyanate concentration of between about 6.5% andabout 11.0% or from a monomer and an addition of isocyanate at aconcentration to achieve substantially the same molal concentration,with a shore D hardness less than about 35%. In a preferred embodiment,the pad is made from a polyurethane mix in which the isocyanateconcentration is between about 6.5% and about 8.5%, resulting in pads onthe softer side of the hardness spectrum.

In developing the inventive method and the inventive pad it wasdetermined that hardness is a significant parameter in predictingscratching. This is illustrated in FIG. 2 where the y-axis is the numberof scratches and the x-axis is the Shore D hardness. The number ofscratches comes from a test developed to elicit scratches in variouscases, even from the softest of pads. The test consisted of using aknown aggressive barrier slurry, which is generally incapable ofremoving copper, and using it to “polish” —at fairly high downforce (4psi)—a pristine blanket copper film in which the number of pre-polishscratches has already been determined. The copper wafer is polished for1 minute and then remeasured for scratches (using dark-field microscopyat low magnification). The increase in the number of scratches is thenplotted:

The graph indicates the desirable hardness of the pad is approximatelyunder 35 on the Shore D scale. The Politex is measured to be 25 on thisscale by the same measurements (indicated on graph), and for reference,the IC1000 is measured to be 56 (indicated on graph) and reported to be55 in information published by Rohm and Haas Corporation.

A planarization figure of merit, called General Planarization Efficiency(“GPE”) was developed to determine exactly what material or materialsgovern planarization. It was determined that GPE is a function of theisocyanate (“NCO”) concentration of the base resin. Resins that fellwithin the 6.5% to 11.0% range delivered high GPE and resins outsidethat range resulted in low GPE. Therefore, a resin from this range isproposed.

In one embodiment, a chemical-inert blown polyurethane is selected forthe inventive pad. Therefore, in accordance with the present inventionthe above described polyurethane polishing pad is proposed as well asthe above described method of removing barrier and buffing.

In various embodiments, a polyurethane polishing pad may comprise anadditive which includes methyl alcohol, or water, or starch of any typeincluding corn starch. The pad can have a thickness of between 10 milsand 200 mils, and preferably of 80 mils.

In accordance with various aspects of an exemplary embodiment of thepresent invention, the pad can be stacked on a subpad or the pad may bea single-layered pad. Furthermore, the pad in accordance with thepresent invention can be grooved or ungrooved, perforated orunperforated.

An exemplary method of manufacturing the pad in accordance with thepresent invention is now presented. First, as with all urethanes, thecomposition begins with either a prepolymer resin with an NCOconcentration of between about 6.5% and about 11.0%, or a polyol and anamount of isocyanate required to achieve the same molal concentration.The prepolymer is preheated to about 100° F., and may be mixed untilsaid temperature is achieved. Additives may then be added as desired.Exemplary additives include initiators such as water, blowing agentssuch as Vazo, catalysts such as a tertiary amine, and surfactants suchas L-6100, and a silicone surfactant typically used to regulate cellsize supplied by Crompton. An exothermic reaction begins once anaccelerant, such as MOCA (4,4′-Methylenebis-[o-chloroaniline]), alsoknown as a chain extender, is added.

In one embodiment, the pad is formed from a mix comprising at least oneof a prepolymer in combination with an isocyanate concentration ofbetween about 6.5% and about 11.0% to achieve a molal concentration, anda monomer in combination with sufficient isocyanate to achievesubstantially the same molal concentration.

Pores may be created either by the incorporation of air during themixing or by the intentional addition of pore creators, such asmicroballoons as taught in Reinhardt, U.S. Pat. No. 5,578,362. The mixis pored into a mold, which may be preheated. While the exothermicreaction is sufficient to bring the temperature of the center of thecake to some 270° F. and thus to a complete reaction, surface coolingmay prevent the outside of the cake from reacting in a reasonable periodof time. Therefore, the cake may be cured in an oven. This is typicallyperformed at a temperature of about 240° F. for about 6 hours. The cakeis then cooled and sliced to fabricate the polishing pads.

After curing, the cake is allowed to cool, and once cooled, it can besliced using, for example, a stationary skiving blade and movable table.Usable slices of the ‘cake’ are then made into pads by applying adhesiveto one face, mounting to a subpad, if desired, grooving the usablesurface, finishing with a smoothing process, inspecting, and/orpackaging the pad.

Often, if a pad can both planarize and pass the scratch-inducing test,then it can also be used in applications where a buff alone is needed.As such, some pads might have additional applications such as post-oxidebuff. Further, one could conceive of other simple non-CMP cleaningapplications commonly carried out in a semiconductor fabricationenvironment.

Again, since the pad planarizes, one could conceive of using it forexample, to remove remaining copper to the barrier. In this case, sinceit is softer than the primary pad it will not have the same long-rangeplanarization. However, if the first copper removal step is done withthe hard pad, the copper surface should be well-planarized, making useof a slightly softer pad feasible. Another potential application of thispad is therefore also primary copper CMP.

In general, and in accordance with further aspects of exemplaryembodiments of the present invention, the pad may be used on any of anumber of substrates, such as a bare silicon wafer, a semiconductordevice wafer, a magnetic memory disk, and/or the like. Furthermore, thepads can be made by any one of a number of polymer processing methods,such as but not limited to, casting, compression, injection molding,extruding, web-coating, and sintering. At least one layer of the padsmay be single phase or multiphase, where the second phase could includepolymeric microballoons, gases or fluids. The second phase could also bean abrasive such as silica, alumina, calcium carbonate, ceria, titania,germanium, diamond, silicon carbide or combinations thereof.

It will be understood that each of the elements described above, or twoor more together, may also find a useful application in other types ofconstructions differing from the types described above. While theinvention has been illustrated and described as embodied in a method ofchemical mechanical polishing, and a pad provided therefore, it is notintended to be limited to the details shown, since various modificationsand structural changes may be made without departing in any way from thespirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this invention.

It will be understood that each of the elements described above, or twoor more together, may also find a use in other applications and in othertypes of constructions differing from the types described above. Whilethe invention has been illustrated and described as embodied in apolyurethane polishing pad and method of producing the same, it is notintended to be limited to the details shown. Various modifications andstructural changes and changes in the selection, design, and arrangementof the various components and steps discussed herein may be made withoutdeparting from the scope of the invention. For example, the variouscomponents may be implemented in alternate ways. These alternatives canbe suitably selected depending upon the particular application or inconsideration of any number of factors associated with the operation ofthe system. In addition, the techniques described herein may be extendedor modified for use with other types of devices. These and other changesor modifications are intended to be included within the scope of thepresent invention.

1. An polishing pad comprising: a pad, wherein the pad comprises aurethane, a starch, and an isocyanate; wherein the urethane comprises abase resin; wherein the starch is configured to both reduce the elasticrebound of the pad and to improve the CMP removal rate of the padcompared to a similar urethane pad that does not include starch; and,wherein the concentration of the isocyanate is within a range of 6.5% to11.0% of the urethane in the pad.
 2. The polishing pad of claim 1,wherein the Global Planarization Efficiency is 75% to 90%.
 3. A methodof improving a removal rate of a polishing pad, at least one layer ofwhich is constructed comprising the steps of producing a body of a padof polyurethane from a mix; introducing into the mix an additive whichdecreases an elastic rebound of the pad so as to increase achemical-mechanical planarization removal rate; and using as theadditive a substance which at least contains a starch.
 4. A polishingpad, at least one layer of which is constructed comprising the steps ofproducing a body of a pad of polyurethane from a mix; and introducinginto the mix an additive which decreases an elastic rebound of the padso as to increase a chemical-mechanical planarization removal rate; andusing as the additive a substance which at least contains a starch.
 5. Amethod as defined in claim 3, wherein said using step includesintroducing substantially one pound of starch in a 25 pound mix toreduce the elastic rebound of the pad by eight percentage points.
 6. Apad according to claim 3 wherein said layer comprises at least one of apolyether urethane, a polyester polyurethane, and a polycarbonate.
 7. Apad according to claim 3 wherein said layer contains abrasive particlesselected from any of silica, alumina, ceria, titania, diamond andsilicon carbide.
 8. A pad according to claim 3 wherein said layercomprises at least one of a filler, and a nylon.
 9. A pad according toclaim 3 wherein said layer is absent abrasive particles.
 10. A method ofimproving planarization of a urethane polishing pad, comprising thesteps of combining a base resin; and introducing in the base resin andan isocyanate to form a urethane polishing pad; and selecting aconcentration of the isocyanate to be within a range of 6.5% to 11.0% ofsaid base resin to obtain a high planarization property.
 11. The methodof claim 10, wherein said selecting step includes selecting aconcentration of the isocyanate within a range of 6.5 to 8.5%.
 12. Themethod of claim 10, wherein said selecting step includes selecting aconcentration of said isocyanate within a range of 8.5% to 11.0%. 13.The method of claim 10, wherein said layer is composed of a polyurethaneselected from the group consisting of a polyether polyurethane andpolyester polyurethane.
 14. The method of claim 10, and furthercomprising the step of combining a plurality of abrasive particles withsaid base resin and said isocyanate, wherein said plurality of abrasiveparticles are selected from the group consisting of silica, alumina,ceria, titania, diamond and silicon carbide.
 15. The method of claim 10,wherein said method does not include the step of urethane polishing padcombining abrasive particles with said base resin and said isocyanate.16. The method of claim 10, further comprising the step of combining afiller with said base resin and said isocyanate.
 17. A urethanepolishing pad, comprising at least one layer having a base resin, andisocyanate introduced in the base resin, wherein a concentration of theisocyanate in the base resin is within a range of 6.5% to 11.0%.
 18. Theurethane polishing pad as defined in claim 17, wherein the concentrationof the isocyanate in the base resin is within a range of 6.5% to 8.5%.19. The urethane polishing pad of claim 17, wherein the concentration ofthe isocyanate in the base resin is within a range of 8.5% to 11.0%. 20.The urethane polishing pad of claim 17, wherein said at least one layercomprises polyurethane selected from the group consisting of a polyetherpolyurethane and polyester polyurethane.
 21. The urethane polishing padof claim 17, wherein said at least one layer contains abrasive particlesselected from the group consisting of silica, alumina, ceria, titania,diamond, and silicon carbide.
 22. The urethane polishing pad of claim17, wherein at least one layer is absent of abrasive particles.
 23. Theurethane polishing pad of claim 17, wherein said at least one layerincludes a filler.
 24. A method of chemical mechanical polishing of acopper film deposited on a surface of a semiconductor wafer, comprisingthe steps of: removing a bulk copper layer to a barrier; removing thebarrier; and buffing, wherein said removing the barrier and buffinginclude using a polyurethane polishing pad having a shore D hardness ofless than about 35% and having a layer made of a mix comprising at leastone of (i) a prepolymer in combination with an isocyanate concentrationof between 6.5% and 11.0% to achieve a molal concentration, and (ii) amonomer in combination with sufficient isocyanate to achievesubstantially the same molal concentration as in (i).
 25. The method ofclaim 24, wherein the pad comprises an additive including at least oneof a methyl alcohol, water and starch.
 26. The method of claim 24,wherein the pad has a thickness between 10 mils and 200 mils.
 27. Themethod of claim 26, wherein the pad has a thickness of between 40 and100 mils.
 28. The method of claim 24, wherein the pad is a singleopen-layered pad.
 29. The method of claim 24, wherein the pad is stackedon and attached to a sub pad.
 30. The method of claim 24, wherein saidpad includes grooves.
 31. The method of claim 24, wherein said padincludes perforations.
 32. The method of claim 24, wherein said layer iscomprises at least one of a polyether polyurethane and polyesterpolyurethane.
 33. The method of claim 24, further comprising introducingin said layer abrasive particles comprising at least one of silica,alumina, ceria, titania, diamond and silicon carbide.
 34. The method ofclaim 24; and further comprising introducing a filler into said mix. 35.A polishing pad for removal of a barrier and buffing after a bulk copperremoval to the barrier in a chemical mechanical polishing of a copperfilm deposited on a surface of a semiconductor wafer, the polishing padhaving a shore D hardness of less than 35% and having at least one layermade of a mix comprising at least one of (i) a prepolymer with anisocyanate concentration of between 6.5% and 11.0% to achieve a molalconcentration, and (ii) a monomer in combination with sufficientisocyanate to achieve substantially the same molal concentration as in(i).
 36. The pad of claim 35, wherein the pad includes an additivecomprising at least one of methyl alcohol, water, and starch.
 37. Thepad of claim 36, wherein the pad is a single open-layered pad.
 38. Thepad of claim 35, wherein the pad has a thickness between 10 mils and 200mils.
 39. The pad of claim 35, wherein the pad has a thickness ofbetween 40 and 100 mils.
 40. The pad of claim 35, wherein the pad isstacked on and attached to a sub pad.
 41. The pad of claim 35, whereinsaid pad includes grooves.
 42. The pad of claim 35, wherein said padincludes perforations.
 43. The pad of claim 35, wherein said layercomprises at least on of polyether polyurethane and polyesterpolyurethane.
 44. The pad of claim 35, further comprising abrasiveparticles comprising at least one of silica, alumina, ceria, titania,diamond and silicon carbide.
 45. The pad of claim 35; and furthercomprising a filler introduced into said mix.
 46. A method of chemicalmechanical polishing of a copper film deposited on a surface of asemiconductor wafer, the method comprising: removing bulk copper to abarrier; removing the barrier; and buffing, and wherein said removingthe barrier and buffing include using a polyurethane polishing padhaving a shore D hardness of less than 35% and having a layer made froma mix comprising at least one of a prepolymer with an isocyanateconcentration of between 6.5% and 8.5% to achieve a molal concentration,and a monomer in combination with sufficient isocyanate to achievesubstantially the same molal concentration.